Magnetron and method of manufacture



Aug. 21, 1951 E. c. OKRESS MAGNETRON AND METHOD OF MANUFACTURE 3Sheets-Sheet 1 711111111451 lllllllIlllllllllllllizeill! 1 Q5 L. I 56 Ii 37 I it 4.

INVENTOR E C OK/FESS ATTOR N EY ,1 1 E. c. OKRESS MAGNETRON AND METHODOF MANUFACTURE 3 Sheets-Sheet 2 Filed Oct 1, 1942 71 :"z 5 7 2 1 75 A as4 IN M Hi ll! INVENTOR EC. U/KEEZS'S BYWMMM ATTOR N EY Patented Aug. 21,1951 MAGNETRON AND METHOD OF MANUFACTURE Ernest Carl Okress, Montclair,N. J., assignor to Westinghouse Electric Corporation, East Pittsburgh,Pa., a corporation of Pennsylvania Application October 1, 1942, SerialNo. 460,376

18 Claims. 1

This invention relates to generators of high frequency electricity, andparticularly those of the type called magnetrons.

V The principal object of my invention, generally considered, is animproved magnetron for energy in the region of ten centimeterwavelengths and a method of manufacture, as well as an improved portionthereof such as the cathode lead assembly.

Another object of my invention is the manufacture of magnetrons by a,method which avoids the necessity of very accurate machining.

A further object of my invention is to simplify and cheapen theconstruction of magnetrons.

.A still further object of my invention is to increase the permissivetolerances in the manufacture of magnetrons.

An additional object of my invention is to pro-' vide an improvedcoupling arrangement for magnetrons.

Another object of my invention is to'provide an improved filteredcathode lead assembly for magnetrons.

A further object of my invention is to provide an improved method ofmanufacturing magnetrons.

Other objects and advantages of the invention, relating to theparticular arrangement and construction of the various parts, willbecome apparent as the description proceeds.

; Referring to the drawings:

Fig. 1 is a sectional view on the line I-I of Fig. 2, in the directionof the arrows, with parts in elevation, of a magnetron embodyingmyinvention.

Fig. 2 is a sectional view on the line II-II of Fig. 1, in the directionof the arrows.

Fig. 3 is an enlarged sectional view of a portion of the magnetron shownin Fig. 2.

Fig. 4 is a view corresponding to Fig. 3, but showing a modification.

Fig.5 is a view corresponding to Fig. 3, but showing anothermodification.

Fig. 6 is a sectional perspective view of a blank from which the bodymember of the magnetron may be manufactured.

Fig. 7 is a perspective view of said blank after a preliminary operationhas been performed thereon.

Fig. 8 is a, transverse sectional view of a hollow generally cylindricalbody portion in which the processed blank of Fig. 7 it to be fitted.

Fig. 9 is a view corresponding to Fig. 8, but showing the blank of Fig.7 in place in the hollow body portion, with soldering materialpositioned for connecting the parts.

Fig. 10 is a view corresponding to Fig. 9, but showing the parts afterconnection and after removing the central core to provide the cathode- 2receiving chamber, completing the resonant cavity.

Fig. 11 is a diagrammatic representation of a multiple slot magnetronembodying my invention, in order to indicate what the dimensions of thefollowing raphs refer to.

Fig. 12 is a diagrammatic representation of a conventional or multiplecavity magnetron, over which the present magnetron is an improvement, inorder to indicate what the dimensions of the following graphs refer to.

Fig. 13 is a graph showing the relationship between the free spacewavelength of the generated energy and the width of the slot for theeight slot type and the eight cavity type magnetrons.

Fig. 14 is a graph showing the relationship between the free spacewavelength of the generated energy and the slot length for the eightslot type and the eight cavity type magnetrons.

Fig. 15 is a graph showing the relationship between the free spacewavelength of the generated energy and the diameter of one of thecavities in the eight cavity type magnetrons.

Figs. 16 and 17 are fragmentary, diagrammatic views corresponding toFig. 1, but showing other modifications.

Resonant cavity magnetrons, such as those in the 10 centimeter range,have previously been constructed exclusively in accordance with thatdesignated 10 in Fig. 1 of the Okress et al. application, Serial No.457,024, filed September 2, 1942 which issued on Jan. 13, 1948 as PatentNo. 2,434,508, that designated 11 in Fig. 1 of the Mouromtseif et a1.application, Serial No. 433,146, filed March 3, 1942 now abandoned, oras diagrammatically illustrated in Fig. 12 of the present case. Suchstructures require very accurate machining with tolerances of the orderof onehalf a thousandth of an inch for dimensions such as the diameter(2a) of the cylindrical cavities, the width -(t) of the slots leadingfrom the anode chamber to said cavities, the radial length (Z) of saidslots and the diameter (21a) of the cathode receiving chamber due to thehigh wavelength sensitivity, as shown by the following table.

Table I .Multiple cavity magnetmns wahvetlength Wahvelcngth WahyclengthA) A) A) s l per s 1ft per s ift per mil change mil change mil change MM in slot in slot in cavity width length diameter Cm. Cm. C'm. l8. 5 l4.4 10. 6 0. 047 0. 037 0. 027

'ten leads 45 and 46.

copper casings 41 and 48 held in place as by ,most clearly in- Fig. 2.

which will now be disclosed. The corresponding wavelength sensitivity isindicated in the following table.

Table II.-Multiple slot magnetrons 1 Ratio independent of number ofslots.

Referring to the drawings in detail, and first considering theembodiment of my invention illustrated in Figs. 1 and 2 thereof, thereis illustrated a magnetron H consisting of a body or anode portion l2 ofoxygen-free, high-conductivit-y copper having generally triangular,trapezoidal or sector shaped selenium copper alloy (described by Smithin A. I. M. & M. E. lech. Pub. No. 870) portions I3, I l, l5, 16,17, l8,l9 and 2t projecting inwardly from the peripheral portion'22and'separated by slots 23, 24, 25, 2B, 27, 28, Hand 3|. All of these slotscommunicate with the central chamber 32 where the oxide coated nickelbase cathode 33 is positioned.

One'of the segments, such as 18, has a recess 34 t which the inner endof the composite coaxial terminal 35 is afilxed, said terminal in thepresent instance having its large and tapering portions formed oftungsten and its small or inner portion formed of electrolytic copperand being enclosed in tubular copper casing 35 having an annular flange31 threaded as indicated at 38 for a coaxial capacitive cable coupling,which may correspond with the threaded-portion 24 of the Rigrod et al.application, Serial No. 454,615, filed August 12, 1942, which issued onSeptember 24, 1946, as Patent No.

2,408,271. This casing36 is desirably threadably connected to a boss 39outstanding from the pe ripheral portion 22 of the device and desirablyformed of similar material. The terminal 35 is' desirably centered withrespect to the casing 35, as by means of a Corning #704 or softborosilicate glass bead 6| between the same and a cylindrical conductormember of Kovar (which is an alloy containing 28.7 to 29.2% nickel, 17.3to 17.8% cobalt, 52.9 to 53.4% iron, not more than .06% carbon, not morethan manganese, and not more than .2% silicon) or other suitablematerial 42, the inner end of which is desirably soldered with eutecticgold-copper solder to a steel ring 19 and the combination soldered tothe flange portion 3'! with BT solder, as shown most clearly in Fig. 1.BT solder melts at about 779 C.,and is 72% silver and 28% copper.

The cathode 33 in the present embodiment is shown as consisting of ahelical tungsten filament 43 enclosed in an electron-emitting housing 44composed of a mixture of oxides of strontium,

barium and calcium on a nickel sleeve and supplied with power f;rom asuitable source by tungs- The leads project through threadablyconnecting reduced terminal portions 49 and 5| tosaid body portion, andsoldering with RT solder after assembly of all parts, as shown RT soldermelts at about 682 C. and is 60% silver, copper, and 15% zinc.

The slotted arrangement illustrated rather than the conventionalcylindrical cavity system previously referred to, permits the use of amore liberal tolerance of the order of one or two thousandths of aninch, as compared with the extremely small tolerance necessary in theconventional construction evident from tables already referred to.

From the theory of multiple slot magnetrons, and considering one witheight slots as illustrated in Figs. 1 and 11, it is known that Ahzdi andAi dtl, in which 5t represents the increment change in slot width and 61the increment change in slot length measured radially. A of courserepresents the wavelength in free space. This shows that Al, or theincrement change in wavelength, is only about four times 6Z,'theincrement change in slot length, as compared with relatively highvariations in wavelengths for changes in slot length and width inconventional cylindrical cavity resonant magnetrons. Furthermore, acomparison of the Tables I and II and a consideration of the graphs ofFigs. l3,- l4 and 15 indicate definitel that the multiple slotted typemagnetron for about 10 centimeter waves, in accordance with myinvention;*--per mits more tolerance for the critical dimensions,controlling the wavelength than thecon'ventional type referred to.

A consideration of the graphs of Figs. 13, 14 and 15 will show clearlywhy the tolerances may be much greater for a slot type magnetron thanfor one of the cavity type. Furthermore, a study of the graphs, whichare comparable as'relating to magnetrons of the same size, althoughthe-cal- -culations on which they are based neglect end effects, inconnection with Tablesi and II, the following conclusions may be drawn.The eight cavity magnetron has a wavelength sensitivity, with regard toslot width, approximately 29% greater than that for slot lengthvariations and approximately 75% greater than that for cavity diametervariations. In contrast the eight slot magnetron has a Wavelengthsensitivity, with reguard to slot length, approximately three times asgreat as that for slot width.

Finally, the eight cavity magnetron is approximately 14.5 times assensitive to slot width variations and approximately 3 /2 times assensitive to slot length variations as the equivalent eight slotmagnetron.

The method of coupling shown in Fig. 1 represents and permits accuratecontrol of the coupling coefficient, since .it is dependent upon theposition of the recess 34 and the coaxial tube or terminal receivingcavity 5?. This, arrangement is superiormechanically and electricallyas, compared with either the end cavityor loop terminal generally usedand illustrated in the Okress et a1. application previously referred to.

A cathode lead assembly is illustratedmore in detail in Fig. 3.Previously, a filter for such an assembly included a cup opening towardthe magnetron or other generator and, with its closed end portionsecured to the lead, as by silver soldering 'on a previously nlckelplated tungstencons ductor over an efiective area. That arrangement hadseveral disadvantages, such as: nickel-plating tungsten; soldering a cupon. a' tungsten. lead which requires special fixtures and the J'Oint'ssometimes turn out to be weak"mechanically; careful orientation, as aspecial fixture is 'required to hold the cup in proper position in thecathode tube or casing and during the process of sealing the lead-inconductor to'the'gl'ass en- 'velope, so that the gap is not too small;and a movement of the tungsten lead in the cathode tube may bend thecup-and therefore throw it out of line so that it is much closer to oneportion of the cathode tube than another, thereby further increasingvoltage breakdown troubles.

The improved construction illustrated in Fig. 3 overcomes all of theabove disadvantages by connecting the filter sleeve 53 to thecathode-lead casing 4'! rather than the lead 45.

Some of the microwave energy in the generator to which the lead assemblyis connected tends to pass out along the insid of the cathode-leadassembly to the exterior because of some coupling of the lead in theelectromagnetic fields in the end cavity of said generator. For reasonsout of place here, this radio-frequency leakage is undesirable and meansare provided whereby it is prevented from escaping from the generatoralong the cathode leads to the exterior.

The radio-frequency energy tending to enter the cathode-lead assembly 54from the magnetron body encounters the filter section 53 which may beformed as a tube of electrolytic copper or similar material. At theannular gap 80 of the quarter wavelength depth section 55 there appearsa very high impedance,

where Z represents the characteristic impedance of the annular chamber55 and Q is expressed by 27r bi (where is the wavelength and R theresistance per unit length) which can be made relatively large bysuitable choice of radial parameters and material composing the walls ofthe annular chamber 55.

Assuming that the impedance looking in the direction of the arrow 56 isnegligible, which is generally correct, we find that while the impedanceat the gap 51 is very high, almost equal to Z or the resulting lowimpedance at the gap 58 is equalto where Z0 is the characteristicimpedance of chamber 59. Hence at the boundary 5! we have theradio-frequency power reflected back into the tube due to themirror-like action of this boundary because of large impedancediscontinuity.

In assembling the cathode-lead casing 41, which may be of copper, thesleeve 6 l, which may be of Kovar or other material which seals readilyto the glass 62, and the preferably electrolytic copper tube filtersection 53, it is to be noted that only one gold-copper eutecticsoldering operation is necessary, as indicated at 63, as the inner endof the Kovar sleeve 6| holds the filter section 53 in place by pressingthe outstandin annular flange portion 64 against the shoulder 65. Thissimple, though effective, cathodelead assembly requires no specialfixtures except for aligning the desirably tungsten lead 45 which isfree of all encumbrances.

Referring now to the embodiment illustrated in Fig. 4, the filtersection 53 may be a spinning and have a hollow cylindrical extension 6|.It may be formed of Kovar or some other material suitable for sealing tothe glass member 62 The section 53* may then be plated with suitablehigh conducting metal, such as copper or silver, before soldering inplace as indicated at 63 When the spinning 53 *-6l is used, the casing41"- may be shouldered as indicated at 65 in Fig. 4, or formed asdesignated at 41 in Fig. 5 without a shoulder and made of suitablematerial so that an annular weld may be formed at 66 between thespinning 53 6l and the casing 41 when a proper adjustment therebetweenis made. Instead of the weld, soldering may be effected as indicated at63*. For Welding, seamless steel tubing may replace copper for makingthe cylindrical portion of the casing 41 as indicated at 66 and 66. Itis evident that with high axial magnetic field strengths required forhigh power, such a structure cannot be used although it is feasible forlow power.

As a further embodiment, the portions 41' and Sl may be formed as acontinuous cylinder with an annular flange 64 of the section 53 weldedor otherwise secured to the inner surface of said cylinder.

Figs. 6 to 10, inclusive, show the parts of the magnetron body duringthe process of manufacture. After the design, I desirably start with acylindrical disk 61 of selenium copper alloy or other similar metal andprovide a threaded centering pocket 68 in one side opposite a centeringcavity 69 in the other. A steel stud is then secured into the threadedportion 68. This blank may then be mounted in a lathe and turned totruly cylindrical form about the centering cavity 69, or otherwiseformed so that the peripheral surface is truly cylindrical about theaxis of said cavity.

The slots 23 to 29, inclusive, and 3| are then cut or milled, asillustrated in Fig. 7, just far enough so that they reach, but do notsubstantially encroach on what will be the cavity 32 in the magnetron,as shown in Figs. 1 and 2. The slotted blank of Fig. '7 and the segmentto form the boss 39 of Fig. 1 are then fitted to the cylindrical shellH, as shown in Fig. 8, to form the assembly illustrated in Fig. 9supported by a fixture, not shown, and secured in place as by means ofBT solder ring or other connecting means I2 running into the spacebetween the outer surface of the blank 61 and the inner surface of theannular member 1| when the whole body is brought to the meltingtemperature of the solder. The boss segment 39 is back of shell 1 I.

The surfaces of the member I I, above and below the surface 13 which isto be connected to the outer surface 14, is desirably slightly cut awayor relieved, as indicated at 15 and 16, to facilitate entry of thesolder or other connecting medium into the clearance space between theparts. It will be understood that this clearance space need only be verysmall and that the connection is effected in a hydrogen furnace or otherheating means where the parts are prevented from undesired oxidation.

After the parts are joined as one, as represented in Fig. 9, the centercore is removed as by proper drilling to provide the cavity 32 as shownin Figs. 1, 2 and 10, after Which'the other parts may be assembled, andRT solder applied in the form of wire wound about the desired region forsoldering, including the upper and lower copper cover members or plates11 and 18 as shown in Fig. 2, with RT solder rings applied at the jointsand the whole assembly exposed in a hydrogen furnace and brought to themelting temperature of the solder.

Referring now to the embodiment of my invention illustrated in Fig. 16,there is shown a magnetron ll consisting of a body or anode portion l2which, like the magnetron H, is desirably formed of copper and hasselenium copper alloy portions [3 M [5%, i6 l1, l8, l9 and 21 projectinginwardly from a peripheral portion 22 and separated by anode cavities orslots 23 2 25 26 21 28 29 and 3H. All of these slots communicate withthe central chamber 32 where a cathode may be positioned, as in thefirst embodiment.

Instead of forming the slots generally rectangular in section or with apair of opposite walls parallel, in the present embodiment I have madethese anode cavities, slots or pockets generally triangular, trapezoidalor sector shaped in section, that is, diverging outwardly or from thecathode cavity 32 and separated by correspondingly shaped portionsprojecting inwardly from the peripheral portion 22. The particulardivergence of the anode cavities is here obtained by making each anodeprojection, l3 Id I5 I6 I1 Hi I9 and Zi with straight side walls which,between their inner and outer ends, converge for an appreciabledistance. The circumferential length of each slot may be greater or lessthan that of the separating partitions l3 to 19, inclusive, and Zidepending on the characteristics desired. The magnetron of thisembodiment may be formed as described in connection with the firstembodiment except that in forming the slots, as shown in Fig. 7, theyare made to flare or expand outwardly, rather than of uniform width.This may be effected by using a correspondingly modified milling cutteror by taking two cuts at the desired angle with respect to one anotherfor each slot. Except as specifically described in connection with thepresent embodiment the same may correspond with that of the firstembodiment, except that the output device used on cylindrical cavitytype magnetrons would be more appropriate.

Referring now to the embodiment of my invention illustrated in Fig. 17,a form of magnetron 1 l is there illustrated consisting of a body oranode portion i2 or" copper having selenium copper alloy portions E314*, [5 I6 ll [8 [9 and 2 l projecting inwardly from the peripheralportion 22 and separated by slots or pockets 23 24 25 26 21 228 5129 and3: slots communicate with the central chamber 32* where a cathode may bepositioned as in the first embodiment, with which this embodiment maycorrespond except as otherwise specifically described.

In the present embodiment the portions projecting inwardly from theperipheral portion 22 are all generally thin and of uniform width, likethe slots 23 to 29, inclusive, and 3| of the first embodiment, so thatthe slots or pockets therebetween are generally triangular, trapezoidalor sector shaped in section, like the portions l3 to 19, inclusive, and2| between the slots of the first embodiment. In all of the embodiments,however, the inner circumferential width of each siot is uniform and maycorrespond with the uniform inner circumferential width of theseparating partitions, notwithstanding the variation in outercircumferential width of these parts, although this correspondence isnot essential.

One advantage of the embodiments of Figs. 16 and 17, as compared withthat of the first embodiment, and especially of the embodiment of Fig.17, is that magnetrons of lighter weight and greater emciency and powercapacity are there- All of these by produced. This is because theimpedance of the generally triangular, trapezoidal or sector shaped slotor pocket at the slotaperture is much higher than that of the slot ofuniform width of the magnetron of the first embodiment, and hence thisslot shape results in a much better match for the electronic fieldimpedance than in the case of the magnetron of the first embodiment. Anadditional advantage of the trapezoidal slot structure is that thewavelength sensitivity with regard to the structural parameters of thecavity is between that of the rectangular slot and the cylindricalcavity structure.

From the foregoing it will be seen that I have provided an improvedmagnetron and method of manufacturing which avoids the necessity ofaccurate machining, simplifies and cheapens the construction, increasesthe permissive tolerances, involves an improved method of coupling, andmakes use of improved filters on the cathode leads.

Although preferred embodiments of my invention have been disclosed, itwill be understood that modifications may be made within the spirit andscope of the appended claims.

I claim:

1. The method of manufacturing magnetrons comprising forming a generallycylindrical body member, cutting therein radial slots from the peripheryonly partly to the center, to leave outstanding projections, fittingsaid body member into a hollow cylindrical member, securing said bodymember projections to said cylindrical member, and removing the centerportion of said body member to provide a generally cylindrical centercavity for reception of a cathode assembly, which cavity communicateswith radial pockets extending to the hollow cylindrical member.

2. The method of manufacturing magnetrons comprising forming a generallycylindrical body member with outstanding circumferentiallyspacedgenerally triangular projections, fitting said body member into a hollowcylindrical member, soldering the engaging peripheral surfaces of saidbody and cylindrical members, and removing the center portion of saidbody memberto provide a generally cylindrical center cavity forreception of a cathode assembly, which cavity communicates with radialpockets extending to the hollow cylindrical member.

3. A filtered lead assembly comprising a lead, a casing through which aportion of said lead extends, a tube coaxial with said casing,coaztially surrounding said lead but spaced therefrom and with a portionspaced from said casing, and having an outstanding annular portiondirectly secured to said casing, and a vitreous closure member united tosaid annular portion and through which said lead is sealed.

4. A filtered lead assembly comprising a lead, a casing through which aportion of said lead extends, a tube surrounding but spaced from saidlead and formed with an outstanding annular flange engaging a shoulderon said casing, a sleeve secured to the outer edge of said casing andholding said flange against said shoulder, and a glass closure memberextending from a portion of said lead beyond said sleeve and sealedthereto.

5. A filtered lead assembly comprising a lead, a casing through which aportion of said lead extends, a metal member surrounding but spaced fromsaid lead and comprising hollow cylindrical portions of differentdiameters united by an intermediate annular portion, means securing saidmember adjacent said annular portion to said casing, and means closingthe outer portion of said metal member comprising a glass sleeve throughwhich the outer portion of said lead projects, the inner portion of saidsleeve being sealed to the cylindrical portion of said member of largerdiameter.

6. A filtered lead assembly comprising a lead, a casing through which aportion of said lead extends, and a metal member surrounding but spacedfrom said lead and comprising hollow cylindrical portions of differentdiameters united by an intermediate annular portion, means securing theportion of larger diameter inside said casing in adjusted position andcoaxially therewith, and a glass closure member sealed to the outer edgeof said portion of larger diameter and the lead which passestherethrough.

7. A magnetron comprising a housing formed as an outer generally hollowcylindrical portion from which inwardly tapering portions projectdefining a central cathode cavity from which generally rectangularchambers extend radially, a cathode assembly disposed in said cavity,leads from the cathode assembly projecting through said hollowcylindrical portion to outside of said housing, and a sleeve surroundingbut spaced from each lead, providing filters for minimizing loss ofpower from the housing.

8. A magnetron comprising a housing formed as an outer generally hollowcylindrical portion from which generally triangular portions projectinwardly defining a central cathode cavity from which generallyrectangular chambers extend radially, a cathode assembly disposed insaid cavity, leads from the cathode assembly projecting through saidhollow cylindrical portion to outside of said housing, casingssurrounding portions of said leads outside of said housing, and a sleevesurrounding but spaced from each lead and with an outstanding portionsecured to the co'responding casing, providing filters for minimizingloss of power from the housing.

9. A magnetron comprising a housing formed as an outer generally hollowcylindrical portion from which inwardly tapered portions projectdefining a central cathode cavity communicating with generallyrectangular chambers disposed thereabout, a cathode assembly disposed insaid cavity, leads from the cathode assembly projecting through saidhollow cylindrical portion to outside of said housing, a terminal leadextending into said housing in a direction generally normal to one ofsaid chambers and with its inner end fixed in a cavity in a wall of saidchamber, and a conductive casing projecting from said housing anddisposed coaxial with respect to said lead.

10. A magnetron comprising a housing formed as an outer generally hollowcylindrical portion from which inwardly tapered portions projectdefining a central cathode cavity communicating with generallyrectangular chambers disposed thereabout, a cathode assembly disposed insaid cavity, leads from the cathode assembly projecting through saidhollow cylindrical portion to outside of said housing, a sleevesurrounding but spaced from each lead providing a filter for minimizingloss of power from the housing, a terminal lead extending into saidhousing in a direction generally normal to one of said chambers and withits inner end fixed in a cavity in a wall of said chamber, and aconductive casing projecting from said housing and disposed coaxial withrespect to said lead.

11. A magnetron housing formed as an outer generally cylindrical hollowportion to which inwardly tapering fiat-sided portions project defininga central cathode cavity communicating with pockets sector shaped incross section and disposed therearound, said cylindrical portionextending axially beyond said fiat-sided portions for connection withcover plates.

12. A magnetron housing formed as an outer generally cylindrical hollowportion of copper to which are attached separately formed fiat-sidedselenium copper alloy portions of uniform width which project inwarddefining a central cathode cavity communicating with pockets sectorshaped in cross section and disposed therearound, said cylindricalportion extending axially beyond said fiat-sided portions for connectionwith cover plates.

13. The method of manufacturing magnetrons comprising forming agenerally cylindrical body portion with outstanding circumferentiallyspaced projections, fitting said body member into a hollow cylindricalmember, securing said body member projections to said cylindricalmember, and removing the center portion of said body member to provide agenerally cylindrical center cavity for reception of a cathode assembly,which cavity communicates with outwardly flaring pockets extending tosaid hollow cylindrical member.

14. A magnetron comprising a housing formed as an outer generally hollowcylindrical portion from which portions project inwardly defining acentral cathode cavity communicating with chambers disposed thereabout,a cathode assembly disposed in said cavity, leads from said cathodeassembly projecting through said hollow cylindrical portion to outsideof said housing, a terminal lead extending into said housing in adirection normal to the central radial plane of one of said chambers andwith its inner end fixed in a cavity in a Wall of said chamber, and aconductor casing projecting from said housing and disposed coaxial withrespect to said lead.

15. A magnetron comprising a housing formed as an outer generally hollowcylindrical portion, from which flat sided portions project inwardlydefining a central cathode cavity communicating with chamberssector-shaped in cross-section and disposed thereabout, a cathodeassembly disposed in said cavity, leads from said cathode assemblyprojecting through said hollow cylindrical portion to outside of saidhousing, a terminal lead extending into said housing in a directionnormal to the central radial plane of one of said chambers and with itsinner end fixed in a cavity in a wall of said chamber, and a conductorcasing projecting from said housing and disposed coaxial with respect tosaid lead.

16. A magnetron housing comprising a hollow cylindrical portion ofoxygen-free high-conductivity copper from which flat-sided walls ofselenium copper alloy project inward in generally radial directionsdefining a central cathode cavity communicating with pockets disposedtherearound.

17. A magnetron housing comprising a hollow cylindrical copper portion,a plurality of flatsided walls of selenium copper alloy encircledthereby axially, shorter than said cylindrical portion, and projectingfrom the inner surface thereof in generally radial directions defining acentral cathode cavity communicating with pockets disposed therearound,and cover members secured to the axially projecting edge portions ofsaid cylindrical portion.

18. A filtered lead assembly comprising a lead, a shouldered casingthrough which a portion of said lead extends, and a tube coaxial withsaid casing, surrounding but spaced from said lead, with an annularportion outstanding from the outer end portion of said tube, in a planetransverse to its axis, and engaging and secured to the shoulderedportion of said casing.

ERNEST CARL OKRESS.

REFERENCES CITED The following references are of record in the file ofthis patent:

Number Number 12 UNITED STATES PATENTS Name Date Samuel Dec. 8, 1936Dallenbach Aug. 30, 1938 George et al. Oct. 1, 1940 Von Baeyer Jan. 20,1942 Litton Dec. 8, 1942 Fisk Nov. 19, 1946 Spencer Nov. 26, 1946FOREIGN PATENTS Country Date Switzerland Oct. 16, 1941 Great BritainJuly 11, 1939

